1. Field of the Invention
The invention relates to ordnance, particularly to an explosive blast shield. More particularly, the invention relates to a composite panel having explosive blast frequency mitigating components and projectile shredding components. The invention is also a method of making a blast frequency control panel.
2. Discussion of the Related Art
Explosive blast attack against people in open areas and in buildings is a challenge in the armor arts. The primary defense against opportunistic blast attack is a perimeter barrier such as a steel reinforced concrete wall. However, explosive blast generates a pressure wave that continues past an ordinary concrete vehicle barrier. If a large explosive load is detonated, the pressure wave can travel with enough force to cause traumatic brain and lung injury to people superficially protected behind concrete walls and inside buildings.
The mechanisms that result in traumatic brain injury have been investigated. Suggested mechanisms include blast compression of body cavities to generate vascular pulses that are transmitted to the brain, skull deflection, explosively-generated piezoelectric charge formation from loading on the bones of the skull, blast induced cerebral spinal fluid cavitation and direct transmission of pressures and blast wave accelerations sufficient to induce injury into the brain. G. J. Cooper investigated the connection between blast frequencies and injury to human tissue. He found that the frequency range of 1000 and 3000 Hz is particularly damaging to lung tissue. This damaging frequency range is referred to in the Drawing as the Cooper Injury Range. This work is reported in G. J. Cooper “Protection of the Lung from Blast Overpressures by Thoracic Stress Wave Decouplers”, Journal of Trauma: Injury, Infection, and Critical Care, vol. 40, no. 3 (1996), incorporated herein by reference. One method of reducing some of the injury to humans would be to limit exposure to blast frequencies in this range.
Investigations of potential barrier panels have identified blast wave couplers and de-couplers. Simple soft foams increased blast damage to the thorax. This damage was attributed to coupling the blast more effectively with the body. However when high impedance materials, such as high Young's modulus and/or density materials, were used as a facing and backed with a low impedance material such as soft foam, blast wave decoupling was observed. Blast decoupling resulted in less internal damage to the human body.
Investigators have found that textiles exhibit differing behaviors in response to blast pressure loadings. Vests comprising certain textile materials altered blast pressure loading on the thorax. One study found that a ballistic fabric vest increased blast associated injury. Another study indicated that blast pressure loading on the body could be reduced if textile fibers were pre-compressed rather than loose assembly.
The scientific literature reports that initiation of lung damage for one-time blast exposure is a function of peak pressure and duration (impulse). We have not found a definitive determination of the mechanism for traumatic brain injury in the relevant scientific literature. It is reported that blast exposure sufficient to cause brain injury may be less than for lung damage.
There is a continuing need in the ordnance shield arts for an effective explosive blast panel. To be fully effective in protecting human tissue, a panel shield must protect against the force of an explosive blast pressure wave and particularly limit exposure to the most damaging blast frequencies.